Stainless steel is much used in the formation of a metal-rubber composite requiring resistances to water or LLC (long life coolant), but when a vulcanization adhesive is directly applied to stainless steel, and when rubber is vulcanization bonded thereto, the resulting stainless steel-rubber composite has poor resistances to water or LLC, and bond peeling occurs, when the composite is subjected to a dipping test.
To overcome such problems, a coating type chromate processing is applied to the stainless steel as a pretreatment to the application of a vulcanization adhesive, thereby improving the resistances to water or LLC. However, the coating type chromate processing involves Cr ions and thus is not preferable from the viewpoint of environmental pollution.
The present applicant has so far proposed various vulcanization adhesive compositions based on alkoxysilanes (JP-A-7-34054, JP-A-7-216309, JP-A-8-209102, JP-A-9-3432, JP-A-9-40916, JP-A-9-132758, JP-A-10-7990, JP-A-10-8021, JP-A-11-1672 and JP-A-2001-226642). These vulcanization adhesive compositions are particularly suitable for bonding to metal surfaces, which have been subjected to chemical, electrochemical or physical surface treatments in advance, but when applied to untreated metal surfaces, the resulting adhesiveness is not better than that of the stainless steel that has been subjected to, e.g. coating type chromate processing.
An under coats for various vulcanization adhesives based on phenol resin are commercially available, but have failed to show satisfactory adhesiveness and water resistance in the bonding to stainless steel.